Muscular Strength and
Endurance
Tom Seabourne, Ph.D.
Muscle Physiology
Muscles consist of many muscle fibers
(cells) connected in bundles
Muscle fibers are made up of myofibrils
Strength training increases the number
of myofibrils and the size of muscle
fibers = hypertrophy
Inactivity reverses the process =
atrophy
Muscular
System
Fit & Well: Core Concepts and Labs in Physical Fitness
Muscular System
Skeletal Muscle Tissue
Muscle Fibers
Slow-twitch fibers
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Fatigue resistant
Don’t contract as rapidly and forcefully as fasttwitch fibers
Rely primarily on oxidative energy system
Fast-twitch fibers
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Contract rapidly and forcefully
Fatigue more quickly than slow-twitch fibers
Rely more on nonoxidative energy system
Motor Units
 Motor units (nerves connected to muscle
fibers) are recruited to exert force
Physiological Effects of
Strength Training
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Increased muscle mass and size of muscle fibers
Increased utilization and coordination of motor
units
Increased strength of tendons, ligaments, and
bones
Increased storage of fuel in and blood supply to
muscles
Improvements in blood fat levels and biochemical
processes
Benefits of Muscular
Strength and Endurance
Improved performance of physical activities
Injury prevention
Improved body composition
Enhanced self-image and quality of life
Improved muscle and bone health with aging
Prevention and management of chronic
disease
Assessing Muscular
Strength and Endurance
Muscular strength assessed by
determining repetition maximum (1
RM), the maximum resistance that can
be lifted once
Muscular endurance assessed by
counting the maximum number of
repetitions of a muscular contraction
Types of Strength Training
Exercises
Static (isometric) exercise = muscle
contraction without a change in the length of
the muscle
Dynamic (isotonic) exercise = muscle
contraction with a change in the length of the
muscle
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Concentric contraction = muscle applies force as it
shortens
Eccentric contraction = muscle applies force as it
lengthens
Types of Dynamic Exercise
Variable resistance = changing load to provide maximal
resistance throughout a joint’s range of motion
Eccentric loading = placing load on a muscle as it lengthens
Plyometrics = sudden eccentric loading and stretching
followed by a concentric contraction
Speed loading = moving a load as rapidly as possible
Isokinetic exercise = exerting force at a constant speed
against an equal force
Creating a Successful
Weight Training Program
Choosing equipment: Weight machines
versus free weights
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Resistance is provided by both types
Exercise machines
 Safer, convenient, and easy to use

Free weights
 Require more care, balance, and coordination
 Strength transfers to daily activities
Applying the FITT
Principle
Frequency = days per week
Intensity = amount of resistance
Time = number of repetitions and sets
Type = strength training exercises for
all major muscle groups
Frequency of Exercise
American College of Sports Medicine
recommends 2-3 days per week

Allow 1 full day of rest between workouts
Intensity of Exercise:
Amount of Resistance
Choose resistance based on your current
fitness level and goals
To build strength
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Lift heavy weights (80% of 1 RM)
Perform a low number of repetitions
To build endurance
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Lift lighter weights (40-60% of 1 RM)
Perform a high number of repetitions
For a general fitness program
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Lift moderate weights (70% of 1 RM)
Moderate number of repetitions
Time of Exercise:
Repetitions and Sets
To build strength and endurance, do enough repetitions
to fatigue the muscles
The heavier the weight, the fewer the repetitions (1-5)
to fatigue = a program to build strength
The lighter the weight, the higher the number of
repetitions (15-20) to fatigue = a program to build
endurance
To build both strength and endurance, try to do 8-12
repetitions of most exercises
Training for Strength versus
Training for Endurance
Fit & Well: Core Concepts and Labs in Physical Fitness and Wellness
Time of Exercise:
Repetitions and Sets
Set = a group of repetitions followed by a rest period
For general fitness, 1 set of each exercise is sufficient
Doing more than one set will increase strength
development
Rest between sets
Type of Exercise
For a general fitness program:
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8–10 different exercises
Work all major muscle groups
Balance between agonist and antagonist
muscle groups
Do exercises for large-muscle groups and
multiple joints before exercises for smallmuscle groups or single joints
Warm Up and Cool Down
Warm up prior to each weight training
session with a general warm-up and a
warm-up for the exercises you will
perform
Cool down after weight training, relax
for 5-10 minutes, lower your heart rate
FITT
Principle
for
Strength
Training
Fit & Well: Core Concepts and Labs in Physical Fitness and Wellness
Making Progress
To start: Choose a weight with which
you can do 8–12 repetitions with good
form
To progress: Add resistance when you
can do more than 12 repetitions
Maintain good form at all times
Track your progress
Sample Workout Card
Fit & Well: Core Concepts and Labs in Physical Fitness and Wellness
More Advanced Strength
Training Programs
Performing more sets of a smaller
number of repetitions with a heavier
weight
Cycle training (periodization) by varying
type and amount of exercise
Consult a coach certified by the National
Strength and Conditioning Association
Weight Training Safety
Use proper lifting techniques
Use spotters and collars with free
weights
Be alert for injuries